1. Field of the Invention
The present invention relates to ballast control for gas discharge lamps, and in particular to digitally controlled electronic ballast in a ballast control network.
2. Description of Related Art
Ballasts have been used for many years as part of lighting systems employing gas discharge lamps, and in particular fluorescent lamps. Fluorescent lamps pose a load control problem to the power supply lines that provide lamp power because the lamp load is non-linear. Current through the lamp is zero until an applied voltage reaches a starting value, at which point the lamp begins to conduct. As the lamp begins to conduct, the ballast ensures that the current drawn by the lamp does not increase rapidly, thereby preventing damage and other operational problems.
A type of electronic ballast typically provided includes a rectifier to change the alternating current (AC) supplied by a power line to direct current (DC). The output of the rectifier is typically connected to an inverter to change the direct current into a high frequency AC signal, typically in the range of 25-60 kHz. The high frequency inverter output permits the use of inductors with much smaller ratings than would otherwise be possible, and thereby reduces the size and cost of the electronic ballast.
Often, a power factor correction circuit is inserted between the rectifier and the inverter to adjust the power factor of the lamp circuit. Ideally, the load in an AC circuit should be equivalent to pure resistance to obtain the most efficient power delivery, for the circuit. The power factor correction circuit is typically a switched circuit transfers stored energy between storage capacitors and the load. The typical power inverter circuit also employs switching schemes to produce high frequency AC signal output from the low frequency DC input. Switching within the power factor correction circuit and the rectifier circuit is typically accomplished with a digital controller.
By controlling the switching in the power factor correction circuit and the power inverter circuit, operating parameters of the lamp such as starting, light level regulation and dimming can be reliably controlled. In addition, lamp operating parameters can be observed to provide feedback to the controller for detection of lamp faults and proper operational ranges.
When a number of lighting systems are to be controlled at the same time, it is possible to network a number of electronic lighting ballasts together for individual or group control. For example, a network of electronic lighting ballasts are connected to a building computer control center to control lighting in various building areas and monitor energy use and other parameters related to specific parts of the building. See for example U.S. Pat. No. 6,181,086 to Katyl et al.
It would be desirable to provide an electronic ballast for a lighting control circuit that is connectable to a network and that can store a variety of lighting profiles that can be updated from the network, and provide further dynamic control on a large scale basis.
The present invention provides a lighting control system using an electronic ballast for controlling a gas discharge lamp. The electronic ballast is connectable to a Personal Computer (PC) and can store various algorithms and lighting profiles that can be updated by the PC. The electronic ballasts can be connected in a network to the PC to define groups of ballasts and lighting circuits for various tasks. Different ballasts can each have specialized lighting profiles loaded into memory for starting, dimming, power control and fault detection.
This software interface is provided to the PC for programming the ballasts and downloading lighting profiles for individual ballasts or define groups of ballasts. Accordingly, the ballasts can be sensed and controlled remotely by the PC. In addition, the PC can be made part of a larger network such as the Internet, to permit observation and control of lighting systems over a wide area in a variety of applications on a remote basis.